If you’re going to travel internationally, you’ll want to let your credit card provider know ahead of time so they don’t automatically flag your first international transaction as fraud.
UPDATE (March 29, 2016): I am not a bank or credit card company, I don’t want to know what your travel plans are, please call the number on the back of your cards.
American Express is pretty sweet in that you don’t need to let them know – they started as “the” travel card for Americans, and it’s still very widely used in business travel. It’s not very useful for most non-business transactions though – like paying for a hostel, or pulling money out of an ATM.
Call your bank and let them know your travel plans in as much detail as you know (I’m going to be in this country on this date, and I’m planning on being home on this date…) They will mark your account so you can continue using it. ATMs also generally offer the best exchange rate, so make sure you’ve got an ATM card that works in the country you’re traveling to! The only issue I’ve ever had is that some of the ATMs in Japan require a 6 digit PIN vs the standard US 4 digit PIN. But, the ATMs at Narita airport and at all 7-11s will take US ATM cards with no problems. In rural Europe, you might run into ATM machines (and automated gas pumps,etc) that will only accept the Chip and PIN card, which only one US bank issues that I know of (Chase) – and it’s kind of in beta. If you need a Chip and PIN card, you can get a pre-paid one through AAA and Travelex. If you’re sticking to the big cities, you shouldn’t need to worry about it.
Other Credit Cards
Some have online travel notification (USAA), others you’ll need to call the issuer. It’s the same as with ATMs, you’ll need to let them know your itinerary. And if you have any authorized users on your account that will not be traveling with you, make sure they know that.
International transaction fees are usually about 3% for most credit cards, but there are several that are designed for frequent international travelers that do not charge the transaction fee (Pentagon Federal is the big one here that charges no fees). American Express charges a 3% transaction fee – despite being a “traveler’s card”. My bank (PNC) will refund any international ATM fee (usually $4), but will charge me 3% if I use it as a Visa card.
Usually, the best option is to pull out as much cash from an ATM as you think you will need at once, where there’s a flat fee on the ATM withdrawal instead of a percentage fee on each use. If you travel a lot, look into the options which do not charge transaction fees. I’ve yet to get a card that is transaction fee free, but I tend to use cash when traveling (except for business expenses, then I expense the 3% transaction fee for the corporate AMEX).